Arnold was born at Laleham, to a family whose members occupied various public service offices. After a private education under his uncle he was, with interruption at Winchester, educated at Rugby where his father had become the celebrated headmaster in 1828. He enjoyed a friendship with the much older Wordsworth and showed early promise in literature, winning a scholarship in 1841 to read Greats at Balliol College, Oxford from where he graduated in 1844. After a brief teaching position, he became secretary to the President of the Council and published his first book of poetry in 1850.
He became an inspector of schools in order to support a marriage that eventually produced six children, three of whom died young. He published several volumes of poetry in the 1850s and was appointed in 1857, for a double term amounting to ten years, professor of poetry at Oxford combining those duties with continued educational inspection which later included continental surveys. He published several educational texts and literary criticism in the follow decades before retiring from inspection in 1886. His urbane, social nature was sadly missed after he suffered a fatal heart attack in Liverpool.
He was an erudite and worthy poet who attempted a modernistic style in sometimes unusual metres and was well regarded by his contemporaries; but he is mostly remembered for Dover Beach.